(I also tryied to play the commented code too but the result is the same)

i have lejos 0.5.0-alpha on brick, on my eclipse i have API downloaded from git and with tag "lejos-ev3 0.6.0-alpha 308fe5e"...I also tryied 0.5.0-alpha tag but the result is the same..where am I wrong?

I had the same problem when I started with Lejos: on the brick the SD.img in version 0.5.0 and using the latest version from EV3 sources via git.

In my case the "solution" was to use the same version for both on SD.img (drivers on the brick) and ev3classes (API to code my programs). The motor example described in Wiki runs with SD.img 0.6 only because the motor classes EV3LargeRegulatedMotor and EV3MediumRegulatedMotor are not part of the version 0.5.0, so there is no driver on the brick to understand the code => Brick freezes.

While using 0.5.0 version of leJOS there is an older Motor API without the EV3 motor classes. This works, but some people including me had freaky jitter effects using motors. With 0.6.0 came up this week the new Motor classes available in ev3clases, and the motor control is smooth and without jitter effects (in my experiments).

Be sure use the 0.6.0 version of leJOS on brick (Menu => Version), then the motors should work with the EV3*RegulatedMotor classes.